Preloading to reduce loads and save steel on topsides and grillage of catamaran systems

ABSTRACT

The present invention reduces loads and saves steel on topsides and grillage of a catamaran system by creating a counteracting moment to offset a sagging bending moment of its self-weight on the topsides during transportation. The present invention can reduce the span of the supports on the topsides on the catamaran float-over barges and move the reaction forces toward inner edges of the float-over barges. The counteracting moment can cause a reduction of stress on the topsides&#39; and grillage&#39;s members caused during the topside offloading and transportation. The stress reduction can result in the members withstanding the additional dynamic load caused by a catamaran system without increasing member sizes adequate for an offloading operation. The reduction results in a significant savings, given the size of a typical topsides for a Spar hull.

CROSS REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO APPENDIX

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention disclosed and taught herein relate generally to Spartopsides installation methods and systems; and more specifically relatedinstallation methods and systems to preloading float-over barges toreduce loads and save steel on topsides and grillage of catamaransystems.

2. Description of the Related Art

A Spar platform is a type of floating oil platform typically used invery deep waters and is among the largest offshore platforms in use. ASpar platform includes a large cylinder or hull supporting a typical rigtopsides. The cylinder however does not extend all the way to theseafloor, but instead is moored by a number of mooring lines. Typically,about 90% of the Spar is underwater. The large cylinder serves tostabilize the platform in the water, and allows movement to absorb theforce of potential high waves, storms or hurricanes. Low motions and aprotected center well also provide an excellent configuration fordeepwater operations. In addition to the hull, the Spar's three othermajor parts include the moorings, topsides and risers. Spars typicallyrely on a traditional mooring system to maintain their position.

Deck or topsides installation has always been a challenge for floatingstructures, particularly in deep draft floaters like the Spar, whichmust be installed in relatively deep water. In the past heavy liftingvessels (“HLV”), including but not limited to, derrick barges have beenused for Spar topsides installations.

In traditional efforts, the topsides of a Spar require multi-lifting,for example five to seven lifts, to install the whole topsides due tothe lifting capacity of available HLV. Due to multi-lifting, the steelweight per unity area of the Spar topsides can be higher than that oftopsides of fixed platforms installed with a single lifting. If theweight of the topsides is reduced, the weight of the Spar hull may alsobe reduced.

Recently catamaran float-over systems have been used to install atopsides onto a Spar platform. A float-over method is a concept for theinstallation of the Spar topsides as a single integrated deck onto itsSpar hull in which the topsides is first transferred from a single bargeonto at least two float-over barges (called “offloading”) andtransported with the float-over barges to the installation site for theSpar hull. At the installation site, the float-over barges arepositioned on both sides of the Spar hull with the Spar hull below thetopsides, the elevation is adjusted between the topsides and the Sparhull, and the topsides is installed to the Spar hull. Installation ofthe Spar topsides to the Spar hull by the float-over method can allow ahigh proportion of the hook-up and pre-commissioning work to becompleted onshore prior to load-out, which can significantly reduce boththe duration and cost of the offshore commissioning phase. Thefloat-over installation method allows for the installation of theintegrated topsides or production deck on a fixed or floating structurewithout any heavy lift operation.

However, to accomplish the catamaran float-over procedure, thefloat-over barges are necessary separated. During loading andtransportation to the desired location for float-over and installationof a topsides on a Spar hull, the catamaran system is subjected toseveral loading conditions primarily due to wave action on the separatedbarges. These loading conditions would not occur with a single bargeloaded with the topsides on deck, but such a single barge arrangementwould not be conducive to a float over installation of the Spartopsides.

FIGS. 1A-1B illustrates two major different modes of loading. FIG. 1A isa schematic top view of a racking load on a catamaran system used toinstall topsides on a Spar hull. FIG. 1B is a schematic end view of alateral bending load on the catamaran system. The figures will bedescribed in conjunction with each other. In general, a catamaran systemincludes at least a pair of barges 115 a, 115 b (generally 115). Afabricated topsides 110 is removably coupled to the barges 115 through asupporting structure, referenced herein as a grillage system 125 a, 125b (generally 125) mounted to the barges 115 a, 115 b, respectively.Different loads 101-102 occur on the catamaran system 100 that are notprevalent in a single barge system. These loads can include (i) rackingmoments 101 a, 101 b (generally 101), as shown in FIG. 1A, where thebarges 115 are prone to twist relative to each other in response to waveloads causing stresses on the system; and (ii) lateral bending moments102 a, 102 b (generally 102), as shown in FIG. 1B, where the barges 115are prone to twist laterally in response to wave loads causing stresseson the system. The catamaran system 100 generally behaves as a rigidbody when it is subjected to head and beam seas. Wave diffraction onsingle body catamaran system 100 has been performed to calculate thehydrodynamic load on this system.

To withstand these different loads particular to a catamaran system, themembers used to construct the topsides and the grillage system arestrengthened generally by an increase in size, adding weight andexpense, compared to a single barge system with the topsides loaded ontothe single barge. Because a topsides is generally a functioningmicro-city suitable for extensive periods for working crews and otherpersonnel, the topsides structure is relatively a significant size. Anoverall increase in size of even a small percentage can become asignificant increase in actual expense.

There remains then a need to provide a catamaran system for a float-overprocedure with a topsides, but more efficiently use the weight andstrength of the members in the catamaran system to reduce weight andcosts.

BRIEF SUMMARY OF THE INVENTION

The present invention reduces loads and saves steel on topsides andgrillage of a catamaran system by creating a counteracting moment tooffset a sagging bending moment of its self-weight on the topsidesduring transportation. The present invention can reduce the span of thesupports on the topsides on the catamaran float-over barges and move thereaction forces toward inner edges of the float-over barges. The size ofthe members of the topsides and grillage that typically would benecessary to withstand the various forces during the float-overprocedure and transporting on the float-over barges to a desiredlocation can be reduced as a result. The counteracting moment can causea reduction of stress on the topsides' and grillage's members causedduring the topside offloading and transportation using supports spanningfrom one barge to the other barge. The stress reduction can result inthe members withstanding the additional dynamic load caused by acatamaran system without increasing member sizes adequate for anoffloading operation. The reduction results in a significant savings,given the size of a typical topsides for a Spar hull.

In at least one embodiment, the invention discloses a method ofpreloading a catamaran system to reduce load and save steel on topsidesand grillages comprising: transferring a topsides onto at least twofloat-over barges (known as “offloading”) to create the catamaransystem; installing sea fastening members; pumping water or installingother ballast into exterior tanks or on the barges' deck of thefloat-over barges to at least partially counteract a wave load createdon the catamaran system; and transporting the catamaran system to alocation near to a Spar hull.

The disclosure provides a method of preloading a catamaran system toreduce loading and material on a topsides for a Spar hull, comprising:transferring a topsides having a weight onto at least two float-overbarges; coupling the topsides with the barges to create the catamaransystem; and adding a ballast to the barges to at least partiallycounteract a sagging bending moment caused by the weight of thetopsides. After the preloading, the catamaran system with the topsidesand float-over barges can be transported to a location for installingthe topsides on the Spar hull.

The disclosure also provides a catamaran system created for a Spar hull,comprising: a topsides adapted to be installed onto the Spar hull; atleast two float-over barges adapted to support the topsides, thetopsides being coupled to each of the barges with the barges beingspaced apart from each other, the barges comprising a ballast adapted tocreate at least a partial counteracting moment to a sagging bendingmoment created by the topsides on the barges.

The disclosure further provides a method of preloading a catamaransystem to reduce loading and material on a topsides for a Spar hull,comprising: transferring a topsides onto at least two float-over barges;coupling the topsides with the barges to create the catamaran system;and applying a pushing-up reaction on the topsides to at least partiallyreduce a sagging bending moment by the topsides' weight. After thepreloading, the catamaran system with the topsides and float-over bargescan be transported to a location for installing the topsides on the Sparhull.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A is a schematic top view of a racking load on a catamaran systemused to install topsides on a Spar hull.

FIG. 1B is a schematic end view of a lateral bending load on thecatamaran system.

FIG. 2A is a schematic end view of an exemplary embodiment of a topsidesbeing offloaded from single transportation barge to two float-overbarges.

FIG. 2B is a schematic top view of a detail portion of the topsides fromFIG. 2A to be coupled with a portion of the grillage system.

FIG. 3A is a schematic end view of an exemplary embodiment of a topsidescoupled to the grillage system of the float-over barges.

FIG. 3B is a schematic top view of a detail portion of the topsides andthe grillage system from FIG. 3A with sea fastening coupled between agrillage top and the topsides.

FIG. 3C is a schematic side view of a detail portion of a brace on thetopsides from FIG. 3A with a link plate in a retracted position.

FIG. 3D is a schematic front view of the brace of FIG. 3C.

FIG. 4A is a schematic end view of an exemplary embodiment of a topsidescoupled to the grillage system of the float-over barges after the singlebarge is removed.

FIG. 4B is a schematic side view of a detail portion of the topsidesfrom FIG. 4A coupled with sea fastening between the float-over barge andtopsides in which a brace is lowered and installed.

FIG. 4C is a schematic front view of a detail portion of the bracebetween the topsides and the float-over barge from FIG. 4B.

FIG. 5A is a schematic end view of the catamaran system with a ballastedpair of barges that are coupled to the topsides.

FIG. 5B is a schematic end view of the catamaran system with analternative preloading on tie down braces that are coupled to thetopsides.

FIG. 6 is a schematic end view of an exemplary embodiment of thecatamaran system without the ballast 150, showing loading calculations.

FIG. 7 is a schematic end view of an exemplary embodiment of thecatamaran system with the ballast 150, showing loading calculations.

FIG. 8 is a chart illustrating the beneficial effect of thecounteracting moment according to the present invention.

FIG. 9A is a schematic end view of the catamaran system floating over aSpar hull.

FIG. 9B is a schematic top view of a detail portion of the topsides fromFIG. 9A with the sea fastening between grillage top and topsidesremoved.

FIG. 9C is a schematic top view of a detail portion of the topsides fromFIG. 9A with the sea fastening between barge and pre-installed brace ofthe topsides removed.

DETAILED DESCRIPTION

The Figures described above and the written description of specificstructures and functions below are not presented to limit the scope ofwhat Applicants have invented or the scope of the appended claims.Rather, the Figures and written description are provided to teach anyperson skilled in the art to make and use the inventions for whichpatent protection is sought. Those skilled in the art will appreciatethat not all features of a commercial embodiment of the inventions aredescribed or shown for the sake of clarity and understanding. Persons ofskill in this art will also appreciate that the development of an actualcommercial embodiment incorporating aspects of the present inventionswill require numerous implementation-specific decisions to achieve thedeveloper's ultimate goal for the commercial embodiment. Suchimplementation-specific decisions may include, and likely are notlimited to, compliance with system-related, business-related,government-related and other constraints, which may vary by specificimplementation, location and from time to time. While a developer'sefforts might be complex and time-consuming in an absolute sense, suchefforts would be, nevertheless, a routine undertaking for those ofordinary skill in this art having benefit of this disclosure. It must beunderstood that the inventions disclosed and taught herein aresusceptible to numerous and various modifications and alternative forms.Lastly, the use of a singular term, such as, but not limited to, “a,” isnot intended as limiting of the number of items. Also, the use ofrelational terms, such as, but not limited to, “top,” “bottom,” “left,”“right,” “upper,” “lower,” “down,” “up,” “side,” and the like are usedin the written description for clarity in specific reference to theFigures and are not intended to limit the scope of the invention or theappended claims. Where appropriate, elements have been labeled with an“a” or “b” to designate one side of the system or another. Whenreferring generally to such elements, the number without the letter isused. Further, such designations do not limit the number of elementsthat can be used for that function.

The float-over catamaran installation of the topsides onto its Spar hullcan involve several major steps. The Figures illustrate various steps ofan exemplary procedure to achieve preloading on a catamaran system thatcan be used to install one or more topsides on a Spar hull. Each figurewill be described below.

A first step is to load the topsides from the fabrication yard onto thedeck of a transportation barge and then tow the transportation bargefrom the fabrication yard to a sheltered location, including, but notlimited to, a quayside location. A quayside location is a structurebuilt parallel to the bank of a waterway for use as a landing place. Asecond step is to transfer the topsides from the transportation barge toat least one float-over barge, and generally at least two float-overbarges, at the sheltered quayside to create a catamaran system that willbe used to install the topsides on a Spar hull.

FIG. 2A is a schematic end view of an exemplary embodiment of a topsidesbeing offloaded from single transportation barge to two float-overbarges. FIG. 2B is a schematic top view of a detail portion of thetopsides from FIG. 2A to be coupled with a portion of the grillagesystem. The figures will be described in conjunction with each other.

A single transportation barge 105 can be loaded with the topsides 110from a fabrication facility and towed and offloaded to the float-overbarges 115 a and 115 b (generally 115) that together with the topsidescreates a catamaran system 100 for towing or otherwise transporting thetopsides to the Spar hull (not shown). The float-over barges 115 aredesigned to provide buoyancy for the load of the topsides 110 andwithstand environmental load of sea and weather conditions during thecatamaran towing of the topsides to the Spar hull.

Each of the two barges 115 has a grillage system, 125 a and 125 b(generally 125). The grillage system 125 generally has an array of beamsand crossbeams with attachment points for the topsides, such asdescribed below. In at least some embodiments, the grillage system isable to withstand the wave load from the topsides for a catamaran towingof Hs up to 5.6 m, where Hs is the significant wave height. Hs isapproximately equivalent to the visually observed height of the wave andthe measurements and calculations for loading of such wave heights wouldbe known to a person of ordinary skill in the art.

The topsides 110 is provided with a fork 130 a, 130 b (generally 130) onthe topsides. The grillage system 125 is provided with a tallinstallation guide pin 131 a, 131 b (generally 131). The forks 130 onthe topsides are designed to guide the float-over barge's grillagesystems 125 to a coupling position with the topsides using theinstallation guide pins 131.

A third step is installing sea fastening members to secure the grillagesystems mounted to the float-over barges with the topsides. The natureof the fastening can create a solid hinge system that is bendable inresponse to loading on the topsides relative to the float-over barges.

FIG. 3A is a schematic end view of an exemplary embodiment of a topsidescoupled to the grillage system of the float-over barges. FIG. 3B is aschematic top view of a detail portion of the topsides and the grillagesystem from FIG. 3A with sea fastening coupled between a grillage topand the topsides. The figures will be described in conjunction with eachother.

The grillage system 125 can provide a number of hingeable couplings toconnect with the topsides. The term “hingeable” coupling is used broadlyand is not limited to a pair of plates rotating about an enclosed pin.For example, a hingeable coupling can include a bendable coupling thatcan flex and bend as needed or one that is constrained significantly inone plane and flexibly located in another plane. Examples are describedherein. Also, it should be appreciated that a person of ordinary skillcould design the grillage system with any number or type of supports andin any configuration to accomplish the goal of creating a catamaransystem 100. As one example, when the fork 130 of the topsides is engagedwith the guide pin 131 on a float-over barge, a locking plate 132 b(generally 132) can be placed on the side of the guide pin opposite thefork 130 and welded or otherwise coupled to the fork to entrap the guidepin therebetween. This coupling of the fork 130 with the locking plate132 restricts the horizontal movement between the topsides and thefloat-over barge, but still allows vertical or bending movement becausethe fork and the locking plate are not welded to the guide pin. Further,the fork can be made of plate steel, such as and without limitation 1inch (25 mm) thick plate, that relative to the size of the topsidesforms a bendable solid hinge 128 a, 128 b (generally 128) that can flexas needed for bending movement of the topsides relative to thefloat-over barges. In general, the topsides fork 130 and guide pin 131will be coupled near a lateral center of gravity 134 a, 134 b (generally134) of the barges 115 a, 115 b, respectively. The center of gravitywill be generally the center of the barges from side to side when thebarges are constructed symmetrically from side to side. The coupling canoccur along the length of the barge at one or more points. When multiplepoints are used to couple the topsides to the barge through thegrillage, the coupling can be made effectively at the center of gravity,for example, where two points might be equidistant from the center ofthe barges, so that the result is an effective coupling though thecenter of gravity.

Further, after the topsides' weight is transferred to the float-overbarges 115, the middle single barge 105 can be pulled out. In general,the single barge 105 can be removed after the topsides is secured atleast horizontally to the barges, such as with the locking plate 132.

In at least one embodiment, the topsides 110 can be supported by atleast four locations with the forks/locking plates and guide pins alongthe length of each float-over barge 115. However, a person of ordinaryskill could design any number of supporting locations and mechanisms forthe topsides 110 on the barges 115.

FIG. 3C is a schematic side view of a detail portion of a brace on thetopsides from FIG. 3A with a link plate in a retracted position. FIG. 3Dis a schematic front view of the brace of FIG. 3C. The figures will bedescribed in conjunction with each other.

Another hingeable coupling at a hinge 129 a, 129 b (generally 129)between the topsides and float-over barges can be made by coupling a tiedown brace 120 a, 120 b (generally 120 and also shown in FIG. 2A)between the topsides 110 and the grillage system 125. The brace 120 caninclude a center tubular member 121 b (generally 121) and a plate 122 b(generally 122). The tubular member 121 can include a slot 124 b(generally 124), shown particularly in FIG. 3C, through which the plate122 is slidably coupled. One or more fasteners 123 b (generally 123)such as wire rope or chain, can secure the plate 122 in a retractedposition in the tubular member 121. Generally, the tie down braces 120are not welded to the barges until the weight of the topsides istransferred from the single transportation barge to the float-overbarges.

The tie down brace 120 can be positioned above a tie down structure 127a, 127 b (generally 127) adjacent the barge inner edge in a retractedposition shown in FIGS. 3C-3D. The brace 120 is generally disposedlaterally inward from the center of gravity 134 of the barges toward acenter of the topsides. In at least one embodiment, the brace 120reduces the length of the supported topsides between the guide pins 131.

FIG. 4A is a schematic end view of an exemplary embodiment of a topsidescoupled to the grillage system of the float-over barges after a singlebarge is removed. FIG. 4B is a schematic side view of a detail portionof the topsides from FIG. 4A coupled with sea fastening between thefloat-over barge and topsides in which a brace is lowered and installed.FIG. 4C is a schematic front view of a detail portion of the bracebetween the topsides and the float-over barge from FIG. 4B. The figureswill be described in conjunction with each other.

After the weight of the topsides 110 is transferred from thetransportation barge to the float-over barges, the brace 120,specifically the plate 122, can be dropped down and welded to the tiedown structure 127 on the barges 115, as shown in FIGS. 4B-4C. Further,the plate 122 can be welded to the tubular member 121, so that thecoupling between the topsides and the grillage system is fixed inlength. In at least one embodiment, the plate 122 can be made of twothin side plates welded to the support structure and one thicker middleplate with stiffeners coupled to the support structure, that relative tothe size of the topsides forms a bendable solid hinge that can flex asneeded for bending movement of the topsides relative to the barges.

The grillage system 125 of supports and braces make the topsides-bargesystem similar to a rigid catamaran with hinged links at sea fasteningmembers, such as the fork 130/locking plate 132 and brace 120, thuscreating the catamaran system 100.

A fourth step is adding ballast to the barges to at least partiallycounteract a sagging bending moment exerted on the barges by thetopsides. The sagging bending moment generally is the mathematicalproduct of the weight of the topsides acting at a support distancebetween the barges, described in more detail herein. The ballast can beadded by pumping ballast into exterior tanks or by placing ballast onthe float-over barges' deck to create a counteracting moment against thesagging moment of the topsides. The ballast can be liquid or solid.Further, the term “adding ballast” is to be broadly construed and caninclude redistributing ballast or other weight on the barge to createthe counteracting moment against the sagging bending moment, describedherein.

FIG. 5A is a schematic end view of the catamaran system with a ballastedpair of barges that are coupled to a topsides. A ballast 150 a, 150 b(generally 150) is loaded into or onto the float-over barges 115 orotherwise coupled thereto. The ballast 150 can be a variety of weightysubstances, including sea water, fresh water, or other liquids. Further,the ballast 150 can be solid ballast. In general, the ballast 150 isinstalled on the float-over barges 115 after the catamaran system 100 isformed with the topsides 110 coupled to the barges 115. The ballast isgenerally preloaded with the barges prior to the barges and topsidesbeing transported to the site of the Spar hull. The extent of preloadingdepends on the barge capabilities of strength and available buoyancy. Ingeneral, the ballast will be loaded along the length of the barge,although in some embodiments, the ballast can be loaded along portionsof the length of the barge.

Generally, the ballast will be loaded laterally outward from the centerof gravity 134 of the barges, which generally will be outward from thecenterlines of the barges when the barges are symmetrically constructed.Loading outward from the barge's center of gravity creates acounteracting moment toward the center of the topsides that provides alifting force to the inside portions of the barge and thence to thetopsides coupled to the barge.

FIG. 5B is a schematic end view of the catamaran system with analternative preloading on tie down braces that are coupled to thetopsides. The topsides and barges can be coupled with the tie down brace120. A jack system 160 can be coupled to the brace. The jack system canexert a pushing reaction load between the inner edge of the barges andthe topsides on each brace to preload the system and reduce the stresson the topsides' members.

FIG. 6 is a schematic end view of an exemplary embodiment of thecatamaran system without the ballast 150, showing loading calculations.The barges 115 are coupled with the topsides 110 to form the catamaransystem 100. The suspended portion of the topsides between the centers ofgravity of the barges is subject to a sagging bending moment due togravity effects on the suspended mass. In general, the sagging bendingmoment applied on the topsides without preloading ballast can berepresented as 0.125 qL², where q is equivalent linear load on deck andL is the distance between coupling locations on the barges (that is, theeffective centers of gravity, which can be the barges' centerlines whenthe barges are built symmetrically across its lateral cross section).The equivalent linear load is the weight of the topsides, assumed to bedistributed evenly across the suspended length L.

FIG. 7 is a schematic end view of an exemplary embodiment of thecatamaran system with the ballast 150, showing loading calculations. InFIG. 6, the ballast 150 having a weight of P on each barge at a distance“a” from the center of gravity 134 creates a counteracting moment 150 asthe mathematical product of P and a or “Pa”, where P is weight ofballast installed on each barge. Thus, with ballast 150 a and 150 b(generally 150), the sagging bending moment is reduced to 0.125 qL²−Pa.With a reduced sagging bending moment, the topsides can be designedlighter and more efficiently.

For example and without limitation, the inventor has determined thatapproximately 100 kg m² or more of steel for the topsides area can besaved with an exemplary Spar topsides weight of about 20,000 metrictonnes (MT). Stated differently, an estimated 5% to 10% increase insteel is typical and understood to be necessary to provide structuralintegrity to the topsides when a float-over process is used. This 5% to10% penalty can be reduced or eliminated with the use and teachings ofthe present invention.

FIG. 8 is a chart illustrating the beneficial effect of thecounteracting moment according to the present invention. The table alsoincludes a moment created by the wave action on the catamaran system,M_(wave), which can be calculated and is known to those with ordinaryskill in the art. The M_(wave) calculation is not believed relevant tothe purposes of the present invention and is only shown to illustratethat broader calculations are needed for determining the ultimate loadsthat the catamaran system 100 will face in actual use, in addition tothe adjustments advantageously afforded by the present invention.

A fifth step is transporting the catamaran system to the location nearto the Spar hull. During this step, the above described loads in FIGS.1A-1B can have serious effects on the catamaran system without eitherproper structure or proper counteracting moments to reduce the loads, asdescribed herein. Before arrival to the location, the Spar hull isballasted down deep enough to leave ample clearance for the topsides 110to float over. Upon arrival, the fifth step can include the mooring andlashing setup between the catamaran system 100 with the topsides 110 andthe pre-installed Spar hull at the site.

FIG. 9A is a schematic end view of the catamaran system floating over aSpar hull. FIG. 9B is a schematic top view of a detail portion of thetopsides from FIG. 9A with the sea fastening between grillage top andtopsides removed. FIG. 9C is a schematic top view of a detail portion ofthe topsides from FIG. 9A with the sea fastening between barge andpre-installed brace of the topsides removed. The figures will bedescribed in conjunction with each other.

A sixth step is transferring the topsides to the Spar hull. In general,a Spar hull 165 is at least partially de-ballasted, such that weight ofthe topsides 110 can be gradually and safely transferred to supports atthe top of the Spar hull. Once at least the partial weight of thetopsides 110 is transferred from the barges 115 to the Spar hull 165,the braces 120 between the topsides 110 and the barges 115 can be cut orthe welds can be removed, for example at locations 172, so that thebrace is uncoupled, as shown in FIG. 9B. After uncoupling the brace, thetopsides 110 is supported primarily at the fork/locking plate locationson the barges 115. The locking plates 132 may be cut, for example atlocations 171, to allow the barges to be pulled away from topsides, asshown in FIG. 9B. The lashing lines can then be detached. Once thebarges are free from the forks 130, the barges 115 can be pulled awayfrom the Spar hull.

Other and further embodiments utilizing one or more aspects of theinventions described above can be devised without departing from thespirit of Applicant's invention. Further, the various methods andembodiments of the catamaran system can be included in combination witheach other to produce variations of the disclosed methods andembodiments. Discussion of singular elements can include plural elementsand vice-versa. References to at least one item followed by a referenceto the item may include one or more items. Also, various aspects of theembodiments could be used in conjunction with each other to accomplishthe understood goals of the disclosure. Unless the context requiresotherwise, the word “comprise” or variations such as “comprises” or“comprising,” should be understood to imply the inclusion of at leastthe stated element or step or group of elements or steps or equivalentsthereof, and not the exclusion of a greater numerical quantity or anyother element or step or group of elements or steps or equivalentsthereof. The device or system may be used in a number of directions andorientations. The term “coupled,” “coupling,” “coupler,” and like termsare used broadly herein and may include any method or device forsecuring, binding, bonding, fastening, attaching, joining, insertingtherein, forming thereon or therein, communicating, or otherwiseassociating, for example, mechanically, magnetically, electrically,chemically, directly or indirectly with intermediate elements, one ormore pieces of members together and may further include withoutlimitation integrally forming one functional member with another in aunity fashion. The coupling may occur in any direction, includingrotationally.

The order of steps can occur in a variety of sequences unless otherwisespecifically limited. The various steps described herein can be combinedwith other steps, interlineated with the stated steps, and/or split intomultiple steps. Similarly, elements have been described functionally andcan be embodied as separate components or can be combined intocomponents having multiple functions.

The inventions have been described in the context of preferred and otherembodiments and not every embodiment of the invention has beendescribed. Obvious modifications and alterations to the describedembodiments are available to those of ordinary skill in the art. Thedisclosed and undisclosed embodiments are not intended to limit orrestrict the scope or applicability of the invention conceived of by theApplicants, but rather, in conformity with the patent laws, Applicantsintend to fully protect all such modifications and improvements thatcome within the scope or range of equivalent of the following claims.

1. A method of preloading a catamaran system to reduce loading andmaterial on a topsides for a Spar hull, comprising: transferring atopsides having a weight onto at least two float-over barges; couplingthe topsides with the barges to create the catamaran system; and addinga ballast to the barges to at least partially counteract a saggingbending moment caused by the weight of the topsides.
 2. The method ofclaim 1, further comprising transporting the catamaran system to alocation for installing the topsides on the Spar hull.
 3. The method ofclaim 1, wherein adding the ballast to the barges comprising adding theballast outwardly from a lateral center of gravity of the barges.
 4. Themethod of claim 3, wherein adding the ballast comprises adding theballast along the length of the barges.
 5. The method of claim 1,wherein coupling the topsides with the barges comprises coupling thetopsides to a grillage system mounted on each barge.
 6. The method ofclaim 5, wherein coupling the topsides with the grillage systemcomprises coupling the topsides at a location that is near a lateralcenter of gravity of the barges.
 7. The method of claim 6, whereinadding the ballast to the barges comprises adding the ballast outwardlyfrom a lateral center of gravity of the barges in a direction distalfrom the topsides coupled between the barges, the weight of the ballastat a distance from the lateral center of gravity at least partiallycounteracting the sagging bending moment.
 8. The method of claim 5,wherein coupling the topsides with the grillage system comprisescoupling a locking plate at least partially around a guide pin installedon the topsides, the grillage system, or a combination thereof tomaintain a lateral coupling of the topsides with the grillage system. 9.The method of claim 5, wherein coupling the topsides with the grillagesystem comprises coupling at least two braces between the topsides andthe grillage system, the barges, of a combination thereof, the bracesbeing disposed inwardly from a lateral center of gravity of the barges.10. The method of claim 9, wherein coupling the braces between thetopsides and the grillage system, barges, or a combination thereofcomprising preloading the braces in a compressive load by adding theballast to the barges prior to transporting the catamaran system to thelocation for installing the topsides.
 11. The method of claim 1, whereincoupling the topsides with the barges comprises hingeably coupling thetopsides with the barges to allow adding the ballast to the barges to atleast partially counteract the sagging bending moment.
 12. The method ofclaim 1, wherein adding the ballast to the barges comprises pumpingfluid into one or more tanks on the barges.
 13. The method of claim 1,wherein adding the ballast to the barges comprises adding solid ballastto the barges.
 14. The method of claim 1, wherein the lateral center ofgravity is disposed along a lateral centerline of each of the barges.15. The method of claim 1, wherein the barges collectively comprisesufficient buoyancy for a weight of the topsides, weight of the barges,weight of the ballast, and wave load during transporting the topsides tothe location for installing the topsides.
 16. The method of claim 1,further comprising: positioning the topsides over the Spar hull; andde-ballasting the Spar hull to transfer the topsides to the Spar hull.17. The method of claim 1, wherein adding the ballast comprisesredistributing a weight of the barges to counteract the sagging bendingmoment.
 18. A catamaran system created for a Spar hull, comprising: atopsides adapted to be installed onto the Spar hull; at least twofloat-over barges adapted to support the topsides, the topsides beingcoupled to each of the barges with the barges being spaced apart fromeach other, the barges comprising a ballast adapted to create at least apartial counteracting moment to a sagging bending moment created by thetopsides on the barges.
 19. The system of claim 18, wherein the ballastis located outwardly from a lateral center of gravity of the barges in adirection distal from the topsides coupled between the barges, theweight of the ballast at a distance from the lateral center of gravityadapted to at least partially counteract the sagging bending moment. 20.The system of claim 187, further comprising a grillage system mounted oneach barge, the topsides adapted to be coupled with the grillage system.21. The system of claim 20, wherein the topsides is coupled to thegrillage system at a location that is near a lateral center of gravityof the barges.
 22. The system of claim 18, wherein the topsides ishingeably coupled with the barges to allow the ballast to at leastpartially counteract the sagging bending moment.
 23. The system of claim22, wherein the topsides is hingeably coupled with the barges with alocking plate to maintain a lateral coupling of the topsides with thebarges.
 24. The system of claim 22, wherein the topsides is hingeablycoupled with the barges with at least two braces between the topsidesand the barges that are bendable and disposed inwardly from a lateralcenter of gravity of the barges.
 25. The system of claim 18, wherein theballast comprises liquid ballast.
 26. The system of claim 18, whereinthe ballast comprises solid ballast.
 27. A method of preloading acatamaran system to reduce loading and material on a topsides for a Sparhull, comprising: transferring a topsides having a weight onto at leasttwo float-over barges; coupling the topsides with the barges to createthe catamaran system; and applying a pushing-up reaction on the topsidesto at least partially reduce a sagging bending moment by the weight ofthe topsides.
 28. The method of claims 27, further comprisingtransporting the catamaran system to a location for installing thetopsides on the Spar hull.